Amniotic fluid in fetal life: physiology and pathophysiology

HighlightsWhat are the main findings?Our study provides novel insights by characterising the antioxidant profiles of amniotic fluid (AF), with a specific focus on superoxide dismutase isoforms (SOD1 and SOD3), glutathione (GSH), and 8-OHdG.AF provides a redox-regulated microenvironment during foetal development of the gastrointestinal tract (GIT).Antioxidant environment of AF is dynamic, undergoing substantial modulation of the oxidative–antioxidative balance throughout gestation.What is the implication of the main finding?Gestational age-specific components of AF, including enzymatic antioxidants such as SOD1, SOD3, and GSH, should be considered in the development of targeted nutritional and pharmacological interventions, particularly for vulnerable populations such as preterm infants and those with congenital gastrointestinal anomalies.Introduction: Amniotic fluid (AF) plays a pivotal role in foetal gastrointestinal development by delivering bioactive factors that support intestinal maturation. However, the redox environment of AF and its potential contribution to foetal intestinal homeostasis remain insufficiently characterised. This study aimed to quantify key antioxidant markers—superoxide dismutase isoforms (SOD1, SOD3), glutathione (GSH), and the oxidative DNA damage marker 8-hydroxy-2-deoxyguanosine (8-OHdG)—in AF across gestational ages and compare them with those in human milk (HM). Methods: AF samples (n = 60) were collected from pregnancies between 15 and 40 weeks of gestation, grouped into preterm (<37 weeks) and term (≥37 weeks). SOD1, SOD3, GSH, and 8-OHdG concentrations were quantified using ELISA. HM samples (n = 45) were similarly analysed. Results: SOD1 and SOD3 in AF concentrations decreased significantly with gestational age (GA) (p < 0.001), while 8-OHdG levels increased (p < 0.001). SOD3 showed a negative correlation with 8-OHdG (p = 0.004). HM contained significantly higher levels of both SOD isoforms compared to AF (AF vs. HM: 35.6 (1.9–172.3) vs. 267.9 (54.6–843.8), p < 0.001 for SOD1 and 1.2 ng/mL (0.1–26.5) vs. 5.5 ng/mL (0.1–300.0), p < 0.001 for SOD3), regardless of GA. Conclusions: Our findings highlight the dynamic nature of the redox environment in AF and its potential importance for foetal GIT development. The disruption of redox balance by preterm birth or inadequate AF intake during foetal life may have long-term consequences for intestinal development and function. These insights provide a foundation for future clinical studies aimed at enhancing neonatal feeding regimens, particularly for preterm infants and those with congenital gastrointestinal disorders.

Aims: Fetal life and environment should be known in the management of the mother, fetus and newborn. Details; Fetal living and environment are very different from postnatal state, and a fetus lives and grows depending the transfer of oxygen and nourishing materials through the placenta, which attached the uterus, and supported by the umbilical cord circulation. Environment temperature is stabilized by maternal body temperature, humidity is nearly 100%, because the fetus is immersed in amniotic fluid. Fetal circulation differs from postnatal one due to placental circulation and no air respiration. Since the fetus grows floating in amniotic fluid, the fetus lives in the condition of no gravity, which supports fetal movements, and the blood circulation in the long umbilical cord vessels. The acoustical and visual fetal capacities were confirmed by sound and light stimulation, and fetal response with fetal movement and FHR acceleration. Conclusion: The fetal life and growth are useful in the fetal monitoring and postnatal preterm infant incubation

Measurements of plasma total and free testosterone (T) levels in human subjects from fetal to postpubertal life showed about twofold higher total T and 15-fold higher free T levels in female fetuses than in female adults. The ratios between the sexes were only moderate in fetal life. Between the 17th and 31st week of pregnancy the ratios (male:female) of total T were found to be 6.6 in week 17, 1.5 in week 22, 2.3 in week 28 and 1.2 in week 31 of pregnancy compared to 16.2 in adulthood. The corresponding ratios of free T were calculated to be 5.6 in week 17, 1.4 in week 22, 0.9 in week 28 and 0.7 in week 31 of pregnancy compared to 34 in adulthood. In amniotic fluids, we measured even an overlapping of T values between the two sexes. The reason for the observed striking difference of T levels between the sexes in fetal and postpubertal life may be the high adrenal activity and secretion rate in fetal life during brain differentiation. In rats, the contribution of adrenals to plasma T levels is only moderate and much smaller than in human beings. As measured in adult female rats, the portion was found to be about 20% only, contrary to about 60% in women. The main sources of T in female rats appear to be the gonads. The mainly gonadal secretion may be the reason that exposure of pregnant rats to stress diminished the T levels in male fetuses, but did not significantly elevate the T levels in females.(ABSTRACT TRUNCATED AT 250 WORDS)

Little is known about the dynamics of bone formation and bone resorption in utero, particularly the normal changes that occur throughout gestation and in clinical situations that result in low bone mass at birth. The objectives of this study were to describe the effects of gestational age on markers of fetal bone turnover, and to investigate whether the reported low bone mass at birth in small-for-gestational-age (SGA) infants and infants of diabetic mothers (IDMs) was associated with biochemical markers of decreased bone formation or increased bone resorption in utero. Bone formation and resorption were assessed by measurement of carboxyterminal propeptide of type I procollagen (PICP) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP), respectively, in 201 amniotic fluid samples. These markers are by-products of type I collagen formation and degradation, respectively, and have been used in the assessment of bone metabolism ex utero. Both PICP and ICTP concentrations in amniotic fluid were inversely associated with gestational age (P < 0.0001). Amniotic fluid concentrations of PICP increased exponentially in relation to infant birthweight (P = 0.008), and SGA infants had lower amniotic fluid PICP concentrations than controls (P = 0.07). The presence of diabetes in the mother was not associated with alterations in amniotic fluid PICP or ICTP concentrations. Although maturational effects on clearance of bone markers from amniotic fluid cannot be excluded, these data are consistent with a high turnover of bone matrix early in fetal life, and a reduction in bone formation when fetal growth is compromised.

Antenatal diagnosis of tetrahydrobiopterin deficiency by quantification of pterins in amniotic fluid and enzyme activity in fetal and extrafetal tissue

Fetuin A Concentration in the Amniotic Fluid of Fetuses with Down Syndrome Background: Fetuin-A is a plasma protein called Alfa 2- Heremans Schmid glycoprotein. During the fetal life, it is the major component of non-collagenous bone matrix. The aim of this study was to examine the probable variation of Fetuin A which is produced by the fetal liver and trophoblastic tissue and found in abundance in the amniotic fluid Methods: Twenty cases in which amniocentesis were performed were included in the study between December 2012 and December 2013. Amniotic fluid samples were collected from women who underwent amniocentesis in the second trimester of pregnancy. Conventional cytogenetic culture was performed and ten fetuses with Down Syndrome (DS) were identified. They were classified as Group 1 and ten fetuses with normal karyotype were classified as Group 2. Levels of FetuinA in the amniotic fluid were measured in each group. Results: Age, gender, gestational age, obstetrics history and body mass index of the cases in Group 1 and Group 2 were similar. Mean amnion fluid Fetuin-A levels in Group 1 was 3.5 ± 0.4 ng/mL and these values were detected to be 4.7 ± 0.7 ng/mL in Group 2. There was statistically significant difference between the mean amniotic fluid Fetuin-A levels of two groups. (P=0.001 from the Mann-Whitney U test). Conclusion: In the present study, amnion fluid Fetuin-A levels were found to be significantly lower in the presence of DS. Decreased Fetuin-A levels may be effective on antenatal and postnatal developments of fetuses with DS. By the clarification of its importance treatment modalities may be developed.

Predominance of l-dopa in fetal plasma and the amniotic fluid during late gestation in the rat

Summary IgA and its subclasses IgA1 and IgA2 were measured in fetal serum and amniotic fluid throughout gestation by hemagglutination inhibition tests. The IgA1/(IgA1 + IgA2) ratio was higher for fetal serum than for amniotic fluid and was significantly higher in the third than in the second trimester in both amniotic fluid and fetal serum. Am2, a genetic marker for human α2 heavy chains, was typed in a number of combinations of maternal and paternal sera, amniotic fluid, and fetal serum. Three families were informative in that Am2 was present in amniotic fluid, was absent from maternal serum, but present in paternal serum. It was concluded that the fetus synthesized IgA2 in utero.

Sulfated iodothyronines including T4-sulfate (T4S) and T3-sulfate (T3S) have been identified in human serum and amniotic fluid. Little is known, however, about the existence of sulfate conjugation of reverse T3 (rT3S) in man. In this report, we employed a novel, sensitive, and specific rT3S RIA to address this question. The rabbit antiserum to rT3S was highly specific; T4, T3, rT3, and 3,3'-T2 showed less than 0.002% cross-reaction with the antiserum. Only T4S and T3S cross-reacted significantly (0.3% and 0.01%, respectively); other analogs cross-reacted less than 0.0001%. The detection threshold of the RIA was 14 pmol/L (1.0 ng/dL). The mean serum rT3S concentration (pmol/L) was 40 in euthyroid subjects. Values were similar in hypothyroid patients (38) and pregnant women (52) but significantly (P < 0.01) elevated to 176 in hyperthyroid patient, 74 in patients with nonthyroid illnesses, and 684 in cord sera of newborns. Serum rT3S increased significantly in hyperthyroid patients 1 day after administration of 1 g sodium ipodate orally. Reverse T3S was detected consistently in amniotic fluid at 14 to 22 weeks of gestation and showed a marked rise 1-3 weeks after intraamniotic administration of 500-1000 micrograms T4. The various data suggest that: (1) rT3S is a normal component of human serum and amniotic fluid; (2) it is derived from metabolism of T4 or rT3; (3) circulating rT3S increases in hyperthyroidism and in circumstances where type I 5'-monodeiodinating activity is low, e.g. nonthyroid illnesses, fetal life, and after administration of ipodate.

To investigate the regulation and physiological significance of SHBG in fetal life, it's distribution in maternal and fetal blood and in amniotic fluid was measured. In spite of high circulating estrogens, the fetal SHBG-levels were 13.4-fold below the maternal blood-concentrations: 3.0 ± 1.0 (SD) ug/ml (n = 62) versus 40.1 ± 9.3 (SD) ug/ml (n = 64). No significant difference was found regarding fetal sex in maternal and fetal blood: female 2.9 ± 0.8 ug/ml (n = 29) and male 3.2 ± 1.0 ug/ml (n = 33). In amniotic fluid the SHBG-concentration was 1.1 ± 0.6 ug/ml in female and 0.9 ± 0.5 in male pregnancies. This difference is not significant. After the sharp fall of estrogens postnatally the maternal SHBG-concentration declined by 50% during the first puerperal week. In contrast, the SHBG-levels increased by almost 100% during the first week in the newborns of both sexes (5.6 ± 1.8 ug/ml). These findings suggest, that fetal and maternal SHBG-levels are independently regulated. While maternal SHBG is strongly influenced by circulating estrogens, the regulation in fetuses and newborns seems to be controlled by mechanisms other than induction and suppression by estrogens and androgens. It may be speculated, that the low SHBG-levels during fetal life are related to the increased biological steroid activity during this period. In contrast to other studies the measurement of SHBG in amniotic fluid did not prove to help identify fetal sex. Supported by the DFG, Grant No. Si 323/2-1

Life in the amniotic fluid

Established facts: Bartter syndrome is a rare heterogeneous group of autosomal-recessive salt-losing renal tubular disorders that can present in fetal life (antenatal Bartter syndrome; ABS) as “unexplained” early-onset polyhydramnios, often associated with growth restriction. Prenatal diagnosis of the condition involves assessment of amniotic fluid biochemistry in a setting of polyuric polyhydramnios; with elevated chloride levels considered a consistent and diagnostic finding. Other amniotic fluid biochemical markers have been described, notably increased aldosterone levels, and low total protein levels. Novel insight: Antenatal Bartter syndrome is a heterogeneous group of renal disorders. While certain biochemical features in amniotic fluid might heighten suspicion, final diagnosis can only be made in the postnatal setting. In the setting of unexplained severe polyhydramnios, clinicians should continue to entertain the diagnosis of antenatal Bartter Syndrome and maintain neonatal surveillance, even if amniotic fluid markers do not support the diagnosis.

Fetal kidney volume and its association with growth and blood flow in fetal life: The Generation R Study

The gastrointestinal tract (GIT) is a complex system, which changes in response to requirements of the body. GIT represents a barrier to the external environment. To achieve this, epithelial cells must renew rapidly. This renewal of epithelial cells starts in the fetal life under the influence of many GIT peptides by swallowing amniotic fluid (AF). Development and maturation of GIT is a very complex cascade that begins long before birth and continues during infancy and childhood by breast-feeding. Many factors like genetic preprogramming, local and systemic endocrine secretions and many trophic factors (TF) from swallowed AF contribute and modulate the development and growth of the GIT. GIT morphogenesis, differentiation and functional development depend on the activity of various TF in the AF. This manuscript will review the role of AF borne TF in the development of GIT.

Methylation metabolism is essential for fetus development. However, normative data for amniotic fluid (AF) concentrations of methylation metabolites at different gestational ages are lacking. We aimed to determine in AF reference values of 14 intermediates involved in methylation. Two hundred sixty-eight AFs sampled between 14 and 39 weeks of gestation were retrospectively selected in our AF bank. Next, we measured methionine (Met)-cycle intermediates [S-adenosyl Met (AdoMet), S-adenosyl-l-homocysteine (AdoHcy), total Hcy, Met, and methyl malonic acid] and methyl donors and methyl acceptors (betaine, dimethylglycine, sarcosine, free and total choline, free and total ethanolamine, creatine, and guanidinoacetate) by liquid chromatography coupled with tandem mass spectrometry. Reference ranges according to gestational age were determined for each parameter. Strong correlations between metabolites directly connected in their metabolic pathway and between total Hcy and betaine were observed. Methionine, an essential amino acid required for protein synthesis, is the only parameter that dramatically decreases with gestational age. The AdoMet/AdoHcy ratio exponentially increases from 25 weeks of gestation, which could reflect increasing methylation capacities. The negative correlation between betaine and total Hcy together with a constant betaine to dimethylglycine ratio during gestation suggests that betaine may be used as a methyl donor during fetal life.